This Windows release is the 64-bit version of the Windows XP
32-bit operation system. The interface is similar to Windows XP but
there are a lot of changes. Microsoft has also updated the Windows XP kernel
which is also partly based on Windows 2003. Windows x64 will
run on the AMD Athlon 64 and
AMD Opteron with AMD64, and the Intel Xeon and Intel Pentium 4 with EM64T.
Windows XP Professional 64-Bit Edition and Windows XP Professional 32-bit
differ in performance and capacity. As a result, the setup, disk space and
device driver requirements also differ. You can't install this version on
a computer that has an x86 (32 bit) architecture. Don't confuse Windows
XP Professional x64 Edition with Windows XP Professional 64-bit Edition. Windows XP
x64 is for x64 systems and Windows XP 64-bit is for Intel Itanium-based microprocessors.

Windows XP Professional x64 Edition only comes in professional
version. (From now on when we refer to Windows XP Professional we mean the
32-Bit version and when we refer to Windows XP Professional x64 Edition we
mean the 64-Bit version).

Below is a comparison table listing the setup requirements
for both Windows XP Professional and Windows XP Professional 64-Bit
Edition.

System Requirements Setup Component

Windows XP Professional

Windows XP Professional x64 Edition

Minimum CPU speed

233 megahertz (MHz)

733 MHz

Recommended CPU speed

300 MHz

N/A

Minimum RAM

64 MB

256 MB

Recommended minimum RAM

128 MB

512 MB

Disk space required for Setup

1.5 GB free

1.5 GB free

Let's take a look at the architectural changes. Below is a
table that describes the architectural differences between Microsoft® Windows® XP
Professional and Windows XP 64-Bit Edition.

Architectural Component

Windows XP Professional

Windows XP Professional x64 Edition

Virtual memory

4 gigabytes (GB)

16 terabytes

Paging file size

64 GB

512 terabytes

Paged pool

470 megabytes (MB)

128 GB

Non-paged pool

256 MB

128 GB

System cache

1 GB

1 terabytes

System Page Table Entry (PTE)

660 MB to 900 MB

128GB

Physical Memory and CPU Limits

32-Bit

64-Bit

Windows XP Professional

4 GB / 1 to 2 CPUs

128 GB / 1 to 2 CPUs

Windows Server 2003, Standard Edition

4 GB / 1 to 4 CPUs

32 GB / 1 to 4 CPUs

Windows Server 2003, Enterprise Edition

64 GB / 1 to 8 CPUs

1 TB / 1 to 8 CPUs

Windows Server 2003, Datacenter Edition

64 GB / 8 to 32 CPUs

1 TB / 8 to 64 CPUs

As we can see, Windows x64 can support a lot more memory than
Windows XP 32-bit Edition. Desktop users may not see big differences, as
few users need more than 4GB of virtual memory. A big advantage we can see
is with the memory subsystem, for example with the Non-paged pool. This pool
is used by the operating system for virtual addresses, which remain in memory
and are not paged out to the hard disk. The bigger the pool, the faster the
operating system operates.

Except that, the additional (and wider) general-purpose registers
of the x64 architecture allow for significant gains in compiler efficiency
and overall application speed. With more registers, there is less need to
write out persistent data to memory, only to have to read it back a few instructions
later. Another gain with the additional, wider registers is faster function
calls. Up to four arguments can be passed in registers to a function which
is a big improvement over the x86 approach of pushing and popping arguments
off and onto the stack for every floating-point operation.

Notice: The current x64 Editions of Windows actually only use
40 bits for addressing memory, yielding an address space of 240 or
16 TB. The theoretical maximum of a full 64-Bits of address space is 264 or
16 exabytes (1.6x1019).

However, a 64-Bit system needs more memory in order to function properly. As we can see from the table below, Windows x64 kernel takes 60% more memory than Windows XP 32-Bit Edition. As a result, in order to gain the same performance level with the 32-Bit, users must upgrade their system memory.

Required Kernel memory

Windows XP Professional

Windows XP 64-Bit Edition

Total

52120 (KB)

31344 (KB)

Paged

40572 (KB)

25396 (KB)

Non-paged

11548 (KB)

5840 (KB)

In the next page we take a better look at the operating system's
capabilities.